The present invention concerns the interconnection of aluminum components, especially but not exclusively the interconnection of aluminum components of heat exchangers by brazing.
It is well known to provide heat exchangers and radiators by interconnecting conduits for primary heat exchange fluid and providing means for circulating secondary heat exchange fluid over the conduits, the external surface area of which is often extended by fixing fins thereto. The fins are normally attached to the conduits by brazing. The conduits and cooling fins are manufactured from aluminum and the brazing process involves joining one to the other with a brazing alloy (Alxe2x80x94Si). The alloy""s melting point is lower than that of the component being joined so that when heat is applied to the joint area it melts, but not the component. A metallurgical bond is thus formed between the components. Normal brazing processes are carried out in:
a) a vacuum atmosphere without flux;
b) a molten salt bath with coating;
c) a protective gas atmosphere with coating and with flux;
d) air with coating and with flux.
The process is often assisted by coating one, other or both of the aluminum components being brazed together with a AlSi 8-12 or additional brazing material e.g. strips, bars or powder.
According to the present invention there is provided a method of interconnecting components of aluminum having a purity of at least 95% comprising brazing the components together and thereafter surface treating assembled components by subjecting them to a Boehmitting procedure.
Preferably the components are brazed together in a dry oxygen containing atmosphere in the presence of the suitable flux or paste.
Preferably at least one component is extruded.
Preferably the atmosphere in which the brazing is carried out is ambient air.
Preferably the brazing flux is an insoluble flux consisting of potassium tetrafluoraluminate with solid foils or particles of aluminum silicate (AlSi10) powder, or coated core material.
Preferably the brazing paste includes potassium tetrafluoraluminate with a constituent creating a thixotrophic characteristic and aluminum silicate (AlSi) powder.
Preferably the components allow a brazing temperature in the range 590xc2x0-625xc2x0 C. simultaneously and remain at this temperature for substantially six minutes.
Preferably the Boehmitting procedure comprises subjecting the components to deionized water at a temperature of about 100xc2x0 C.
Alternatively the Boehmitting procedure comprises subjecting the components to wet steam at a temperature of about 150xc2x0 C.
Preferably the assembled components are further surface treated by a solution of silicate of sodium (Na2SiO4) in water at about 90-100xc2x0 C.
Alternatively the assembled components are further surface treated by:
a) subjecting them to 10% boracic acid at about 80-100xc2x0 C. mixed with water or;
b) subjecting them to 5-10% borax at about 80-100xc2x0 C. mixed with water or;
c) subjecting them to waterglass (Na2SiO4) at about 90-100xc2x0 C. mixed with water or;
d) subjecting them to a low viscosity resin coating.
Preferably the Boehmitting procedure is carried out only on the material surface of the conduit.